The gamete that contains genes contributed only by the mother is the egg cell or ovum.

Here's why:

* Egg cells (ova) are produced through a process called oogenesis, which occurs within the ovaries of the female.

* Sperm cells, on the other hand, are produced through spermatogenesis in the testes of the male.

* During fertilization, a single sperm cell fuses with a single egg cell, contributing their respective genetic material.

Therefore, the egg cell carries only the mother's genetic contribution, while the sperm cell carries only the father's genetic contribution.